core/thread: "fix" valgrind errors in thread_measure_stack_free() #20726
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benpicco merged 1 commit intoRIOT-OS:masterfrom Jun 5, 2024
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core/thread: "fix" valgrind errors in thread_measure_stack_free() #20726benpicco merged 1 commit intoRIOT-OS:masterfrom
benpicco merged 1 commit intoRIOT-OS:masterfrom
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The dark magic used used in thread_measure_stack_free() is frowned upon by valgrind. E.g. valgrind may deduce (by monitoring the stack pointer) that a specific value was at some point allocated on the stack, but has gone out of scope. When that value is now read again to estimate stack usage, it does look a lot like someone passed a pointer to a stack allocated value, and that pointer is referenced after that value has gone out of scope. This is "fixed" by temporarily disabling valgrind error reporting while iterating over the stack.
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Contribution description
The dark magic used used in thread_measure_stack_free() is frowned upon by valgrind. E.g. valgrind may deduce (by monitoring the stack pointer) that a specific value was at some point allocated on the stack, but has gone out of scope. When that value is now read again to estimate stack
usage, it does look a lot like someone passed a pointer to a stack allocated value, and that pointer is referenced after that value has gone out of scope.
This is "fixed" by temporarily disabling valgrind error reporting while iterating over the stack.
Testing procedure
Testing that this indeed "fixes" the warning
With this PR:
With #20723 (with current
masterthe function is broken and doesn't iterate over the stack - hence, no errors):(That one context is
thread_measure_stack_free().)Confirming that suppression is reasonable
Double check my reasoning why, in this specific instance, the access of stack memory is not an error.
Issues/PRs references
Depends upon and includes: